The invention relates to a method for controlling the filling of gas cylinders.
In the present invention, the terms “cylinders” and “tanks” which designate hermetically sealed containers for storing pressurized gas, are used as equivalents.
Since environmental conservation is becoming an increasingly pressing concern both for industrial companies and for private individuals, demand for “clean” fuels for motor vehicles is steadily growing.
One possible alternative for replacing conventional fuels is the use of gas.
However, while filling a tank with gasoline or fuel oil, which are liquid fuels, is an easy and rapid operation, filling tanks with gas is a much more delicate operation. Owing to the compressibility of gases, the filling can lead to considerable temperature rise and also raises the problem of “metering” the quantity of material transferred.
In fact, the gas must be injected from a gas storage zone into pressurized gas tanks or cylinders (200 bar or more depending on the gas and the application); the storage zone is itself under high pressure or under low pressure, in which case it is necessary to use a compressor.
For safety reasons, the final pressure in the tank, as well as the temperature of the gas in the tank and the mass of gas stored, must not exceed the tank strength limits as determined by the manufacturers of said tanks. Moreover, the faster the filling, the greater the temperature rise, and hence the more difficult it is to optimize the quantity of gas inside the tank.
Tanks are accordingly very often filled below their capacity, filling occurs more frequently, and consumption is difficult to assess, providing a source of discomfort for the user.
Furthermore, it must be observed that the gas temperature inside the cylinder is very difficult to obtain because it would require the installation of a temperature probe placed directly in the cylinder, with all the sealing problems that this implies, and a connection between the vehicle and the storage station for the exchange of data.
Obviously, the same difficulties arise for the supply of gas to all types of tanks or cylinders.
Conventionally, the filling takes place at ambient temperature, using the principle whereby the measured parameters are controlled and/or the maximum values of these parameters are estimated, that is, the pressure and/or temperature, using the onboard temperature measurement, that is, the measurement of the gas temperature in the cylinders, as in patent applications EP1205704 and EP1336795, or by using the measurement of the mass injected, obtained by weighing (U.S. Pat. Nos. 4,527,600, 4,648,430, 5,791,947, 5,771,948, 5,810,058, 5,881,779) or by measuring the flow rate (U.S. Pat. Nos. 4,993,462, 5,238,030, 5,752,552).
Furthermore, another method for overcoming the problem of insufficient filling consists in cooling the gas entering the cylinder to a temperature set at a value below the ambient temperature, as described in patent application EP1331289. However, the temperature selected is not optimized and does not represent a comprehensive solution for the optimal and safe filling of the cylinders.
Document EP 1 452 794 A2 describes a filling method at a rate depending on the ambient temperature, the filling being interrupted when the temperature measured in the tank reaches a maximum limit.
Document U.S. Pat. No. 5,628,349 describes a filling method and a filling rate which depends on the gas temperature measured in the tank.
Document U.S. Pat. No. 6,598,624 describes a filling method in which the filling rate is adjusted according to the instantaneous pressure measured in the tank.
All the methods described are either difficult to implement because the parameters to be measured are relatively inaccessible, particularly the internal temperature of the gas, or are inappropriate for certain applications, such as weighing for the vehicle application, or use measurement means which lack accuracy in certain cases, particularly instruments for measuring the mass flow rate in the case of hydrogen, so that the maximum temperature in the cylinder is not controlled, or which do not permit optimization of the filling.
Thus a real need exists for a method for controlling the filling of gas cylinders or tanks which is at once reliable regardless of the data available to the operator, and particularly when he cannot determine the temperature in the tanks, easy to implement, easy to use and suitable for any type of cylinder and any type of filling, particularly for rapid fillings.